from the Island of Malta. 263 



single interambiilacrum elevated into a prominent carina ter- 

 minating in a caudal hooked process. 



Description. — This Urchin resembles Schiz aster canaliferus 

 now living on the shores of the Mediterranean, and for which it 

 has been mistaken by some naturalists, but an attentive study of 

 the living and fossil species discloses characters by which they 

 may be distinguished from each other. The test in S. eurynotus 

 is cordate, depressed before and elevated behind. The ambu- 

 lacral areas are deeply depressed; the odd or anterior ambu- 

 lacrum is nearly twice the width of the pairs, it swells out in the 

 middle, is blunted at the apex, and most contracted at the 

 anteal sulcus, which is deep and narrow when contrasted with 

 the width it attains above. The poriferous zones lie at the base 

 of the walls of the sulcus ; the very narrow plates that compose 

 the floor of this area are each studded with a row of small gra- 

 nules. The antero-lateral ambulacra diverge at an angle of 52°; 

 they are slightly /-shaped, and are l^^ inch in length : the 

 numbers of holes in the zones are thirty-six and thirty-four. 

 The postero-lateral pair are short, and make an angle of 72°; 

 they are y'^ths of an inch in length, and have respectively 

 twenty-six and twenty-four holes in their zones. The peripetal 

 fasciole passes close to the base of the posterior pair, dips slightly 

 into the space which separates the anterior from the posterior 

 pair, runs at some distance from the anterior pair, passes close 

 by the base thereof obliquely towards the anteal sulcus, into 

 which it dips, and meets its fellow from the opposite side : the 

 very narrow postero-lateral fasciole is directed obliquely down- 

 wards and backwards, and unites with its fellow at some distance 

 below the anus. The test is depressed anteriorly and sloped 

 away at the cheeks, whilst behind it is much elevated. The 

 interambulacrum forms an elevated ridge between the posterior 

 ambulacral pair, and is produced into a caudal-like process 

 behind, beneath which the circular anus is pierced ; the sternal 

 portion of the odd interambulacrum is tumid and convex ; the 

 basal portions of the lateral and anterior pairs slope gently 

 towards it ; the tracks of the ambulacra are nearly naked as they 

 approach the mouth, and are here perforated with buccal pores. 

 The mouth is at the anterior third, and has a projecting under- 

 lip; the tubercles on the upper surface are small and of a 

 uniform size ; those on the sternum are larger, and are per- 

 forated and set on crenulated summits; they are arranged in 

 lines radiating from a posteal point ; the tubercles of the inter- 

 ambulacral pairs are the largest. 



Affinities and differences, — This species very much resembles 

 the living >S. canaliferus, but it may be distinguished from it by 



